986 Forum - The Community for Porsche Boxster & Cayman Owners - View Single Post - Interpreting OBD data

Legba · 10-08-2012, 02:43 AM

Sorry if this is a bit long but.....

I am trying to interpret some data to track down a misfire and need some help to interpret live OBD data on my 1998 2.5 Boxster (UK spec).

Can anyone tell me what the following means?

STFT (Short Term Fuel Trim) and
LTFT (Long Term Fuel Trim)

At times I have seen STFT vary from 0 to 25%. Presumably the readings for B1 and B2 should mirror each other.

I also have readings for:
SHRTFT
SHRTFT 12
SHRTFT 22

What do they mean? What is the difference between STFT and SHRTFT?

The readings obviously vary depending on driving conditions but a snapshot I got was:

STFT B1 18.75%
LTFT B1 0.78%
STFT B2 18.75%
LTFT B2 0.78%

SHRTFT = 0%
SHRTFT 12 = 99.21%
SHRTFT 22 = 99.21%

I also have readings for O2S which I assume is the voltage of the O2 sensors.

What does the following mean?

O2SL 11 12 21 22
O2S11 = 0
O2S12 = 0.435
O2S 21 = 0
O2S 22 = 0.435

Grateful for any help.

10-08-2012, 02:43 AM	#1
Legba Registered User Join Date: Sep 2012 Location: Ipswich UK Posts: 16	Interpreting OBD data - What does it Mean? Sorry if this is a bit long but..... I am trying to interpret some data to track down a misfire and need some help to interpret live OBD data on my 1998 2.5 Boxster (UK spec). Can anyone tell me what the following means? STFT (Short Term Fuel Trim) and LTFT (Long Term Fuel Trim) At times I have seen STFT vary from 0 to 25%. Presumably the readings for B1 and B2 should mirror each other. I also have readings for: SHRTFT SHRTFT 12 SHRTFT 22 What do they mean? What is the difference between STFT and SHRTFT? The readings obviously vary depending on driving conditions but a snapshot I got was: STFT B1 18.75% LTFT B1 0.78% STFT B2 18.75% LTFT B2 0.78% SHRTFT = 0% SHRTFT 12 = 99.21% SHRTFT 22 = 99.21% I also have readings for O2S which I assume is the voltage of the O2 sensors. What does the following mean? O2SL 11 12 21 22 O2S11 = 0 O2S12 = 0.435 O2S 21 = 0 O2S 22 = 0.435 Grateful for any help.